Best Off-Grid Solar Kit for a Cabin, Shed or RV (Sized by Daily Watt-Hours)

Start with watt-hours per day: each load's watts x hours of use, with fridges and freezers at their duty cycle (a 150 W fridge running a third of the time is about 1,200 Wh a day). Then three steps, the same ones our off-grid solar calculator runs.

1. Battery draw. Divide the AC watt-hours by 0.9 for inverter losses. A 2,000 Wh day draws about 2,222 Wh from the battery.

2. Battery bank. Multiply by the days you want to ride through without sun, then divide by 0.9 so the bank never drops below 10%. Two days of 2,222 Wh is about 4,938 Wh of LiFePO4 nameplate.

3. Panels. Divide the daily battery draw by your sun hours x 0.78. The 0.78 covers wiring, dust, heat, mismatch and charging losses (PVWatts' 14% system loss, then 95% battery and 96% controller efficiency). In Albany, NY, the worst summer month gets 4.7 sun hours, so 2,222 / (4.7 x 0.78) = about 603 W, four 200 W panels. The worst winter month gets 2.2, so the same cabin needs about 1,288 W, seven panels.

That winter-to-summer gap is the most common sizing mistake. If the cabin closes from November to March, size for the summer number. If someone lives there year-round, size for winter or plan on a generator for the darkest weeks. Phoenix stays at 4.9 sun hours even in its worst month; Seattle drops to 1.7.

A power station is battery, inverter and MPPT charger in one case. You plug panels into its solar input and appliances into its outlets. Nothing to fuse or crimp, it comes home with you, and it doubles as outage backup.

Its limit is the solar input rating. Daily refill is about input watts x sun hours x 0.78, and only if you buy enough panels to reach it. A 1,000 W input with five 200 W panels returns about 3,700 Wh on a 4.7 sun-hour day and about 1,700 Wh on a 2.2 sun-hour winter day. Check the station's input voltage range before wiring panels in series.

For the 2,000 Wh a day cabin above with one day of reserve, you need about 2,470 Wh of battery. The Nature's Generator Lithium 3600 covers it alone. The BLUETTI AC200L and Anker SOLIX C2000 Gen 2 cover it with one expansion battery.

Separate parts cost less per watt-hour and let you grow one piece at a time. 12 V suits a shed, van or RV house system. Once the inverter passes about 1,000 W, 24 V halves the battery current, which means thinner cable and smaller fuses.

A shed that uses 500 Wh a day (lights plus an hour of tools) in Denver's worst winter month, 4.2 sun hours, needs about 169 W of panel and 617 Wh of battery for one day. The kit: one 200 W panel, a 40 A MPPT controller, one 12 V 100 Ah LiTime battery and a 1,000 W inverter, plus the Class T fuse, cables and controller fuse, about $500 to $1,000 in all.

The 2,000 Wh a day cabin in an Albany summer moves to 24 V: four panels in series (about 95 V, under 137 V on a cold morning), a 60 A controller, two 24 V 100 Ah batteries on bus bars (5,120 Wh) and a 2,000 W inverter, about over $2,000 with fuses and cables.

An all-in-one inverter/charger has the MPPT built in and runs from a 48 V bank. One box replaces the controller and inverter, and 48 V keeps battery current low enough for a 3,500 to 6,000 W inverter.

The same 2,000 Wh cabin, lived in through an Albany winter, needs about 1,288 W of panels. The Growatt 3,500 W needs at least 120 V from the array to charge, so all seven panels go in one series string: about 166 V running and 239 V on a cold morning, inside its 280 V limit. One 5,120 Wh ECO-WORTHY rack battery holds the two days. Total about over $2,000 with the fuse and cables.

A string over 150 V DC is a shock hazard well beyond a 12 or 24 V system. Use a DC disconnect, never pull MC4 connectors under load, and have an electrician wire the array and the AC side.

If the cabin has a 240 V well pump or appliance, the Growatt SPE 6000 gives 120/240 V split phase from the same 48 V bank, with two MPPT inputs and up to 9,000 W of panels.

Sizing panels for July when you use the cabin in January. Use your worst month's sun hours.

Charging LiFePO4 below 32 F. In an unheated cabin or shed, keep the bank in an insulated box or a room that stays above freezing, or use a power station indoors.

Electric heat and cooking. Space heaters, ranges, water heaters and dryers are the hardest loads for off-grid solar. Propane or wood for heat and cooking usually cuts the system to a fraction of the size.

Skipping the main fuse. A LiFePO4 bank can deliver thousands of amps into a short. A Class T fuse within 7 in of the battery positive (ABYC E-11) is the part that prevents a fire.